This invention relates to an automatic focusing system and in particular to an automatic focusing system for utilization in a combined television and surgical microscope apparatus.
Essentially, the prior art is replete with a number of patents and disclosures relating to automatic focusing devices which devices are utilized in many applications such as photographic cameras, television cameras, and so on. Many prior art patents and apparatus have attempted to measure the quality of focus by measuring the amount of high spatial frequency content in a viewed scene. In such systems there is a problem in obtaining focusing due to the fact that with a moderate or high content the system requires a large dynamic range in order to achieve accurate focusing. The various examples of such systems have been employed in the prior art.
Basically, there are many techniques employed for implementing and achieving focusing in the optical field. For example, U.S. Pat. No. 3,643,574 entitled Focusing Device for Optical Equipment issued on Feb. 2, 1972 to H. Moriyami. This patent shows a focusing system for a movie or television camera. The patent describes a mechanical system using a switching reflector which is mounted so that it can be moved in or out of the optical path of the camera. The reflector is moved into the optical path of a view finder when the camera is being focussed and is moved out of the path after focusing has occurred.
U.S. Pat. No. 3,699,248 entitled Automatic Area of Interest Television Optical Probe Focus Apparatus issued Oct. 17, 1972 to John C. McKechnie. This patent depicts a system where focusing is achieved in regard to a particular scene that a viewer is watching. The apparatus provides focusing by using the video signal of a television camera which signal is used to adjust a lens system which lens system is connected to motors for movement of the same. The control signal for the motors is developed by a frequency discriminator whose output is a function of the frequency of the video signal. The apparatus uses a delay circuit which operates in conjunction with two successive samples of the signal to drive the motors until proper focusing occurs.
U.S. Pat. No. 3,728,482 entitled Focusing issued on Apr. 17, 1973 to J. F. Wren. This patent describes a focusing system for a television camera. The video signal from the camera is band limited so that the high frequency content of the signal is retrieved. This signal is rectified and integrated in first path. The video signal is also directed to a threshold detector which operates with a counter to provide a pulse indicative of a scan line. The apparatus attempts to normalize the high frequency signal to obtain a control signal used for automatic focusing.
U.S. Pat. No. 3,967,056 entitled Automatic Focusing Apparatus issued on Jun. 29, 1976 to K. Yata, et al. This patent describes a focusing system employing a video signal which signal is applied to a maximum and a minimum value detector. The detectors produce signals indicative of a minimum and a maximum signal during a scan. The difference or ratio between the signal values is determined. This is indicative of a focus setting when the difference signal reaches an extreme value manifested by the interuption of movement of the lens assembly.
U.S. Pat. No. 4,317,135 entitled Focus Detection Circuitry issued Feb. 23, 1982 to M. C. Pitruzzello. This patent describes a focus meter which employs a video signal emanating from a television camera. The signal is differentiated and peak detected. A portion of the signal is coupled from the amplifier to a sync separator circuit which causes a gate signal to be generated to disable the differentiator for blanking pulse. The circuit operates to provide a peak signal which is applied to a volt meter. The output of the volt meter is indicative of a proper focus. Thus, as can be seen, the above techniques and others describe various methods for providing automatic focusing which employs a video signal and which use a particular frequency portion of the signal, such as the high frequency portion, to develop a control signal for focusing a lens assembly. In any event, there are difficulties in regard to these techniques and in many of the prior art techniques in that focusing is not reliably achieved due to the detection of the high frequency components and due to various techniques of controlling the lens assembly.
In the system to be described, automatic focusing is employed to control the focus of a microscope which is associated with a television system. In this system the output of the microscope is displayed on a television screen with the system particularly adapted for use in the operating room environment. In this manner the microscope is employed to enlarge an area upon which an operation is being performed, and the optical system enables the viewed area to be displayed upon the screen of a television receiver.
In regard to such considerations, the image must be properly focussed and frequently refocussed because the object change or movement in order for this participants to accurately view the area during the surgical procedure. It is further apparent that an accurate representation of the area is necessary in order to enable students and others to optimumly visualize the procedures involved. Hence focusing quality is of prime importance in such a system. It is, therefore, an object of the present invention to provide an automatic focusing system particularly useful with an operating room microscope and a televison camera to enable accurate and reliable focussing. An additional object is to achieve automatic focus in a very short time. Using the slope technique as opposed to a point by point plot of the detector output, with the maximum determined after a complete plotting. The maximum in this slope technique is reached quickly by detecting when the maximum is being approached and retreated from.